The Westinghouse eVinci microreactor achieved zero-power criticality on August 24, 2025, at 10:39 a.m. local time, at the Nevada National Security Site. A long-anticipated milestone, it moves the project one concrete step closer to commercial deployment.
The test was conducted at the National Criticality Experiments Research Center, a facility of the National Nuclear Security Administration, in collaboration with Los Alamos National Laboratory and Idaho National Laboratory. Zero-power criticality produces neither heat nor electricity: its purpose is to validate the computational models and core design assumptions without initiating a self-sustaining reaction at full power. In essence, it is proof that the calculations hold up against real-world physics. Westinghouse noted that the results from this test campaign will inform future design improvements, prototyping, and manufacturing of the eVinci.
Westinghouse Chief Technology Officer Lou Martinez Sancho thanked the partners, including the U.S. Department of Energy, and stated that the achievement “reflects Westinghouse’s legacy of innovation and pushing toward the next frontier of nuclear energy.” The broader context is the DOE’s Reactor Pilot Program, established under Executive Order 14301 in June 2025, which set a goal of at least three advanced private reactors achieving criticality by July 4, 2026. The eVinci joins a growing list of recent milestones: Deployable Energy’s Unity Nuclear Battery had reached zero-power criticality on June 30 at Idaho National Laboratory, Aalo Atomics on July 4, and Oklo on August 5.
eVinci is a heat pipe-cooled microreactor with a diameter of less than three meters, capable of producing up to 5 MWe from a 15 MWth thermal core. It has no moving parts, can operate for more than eight years without refueling, and the entire system is transportable on a standard semi-trailer. Intended applications range from remote communities and military bases to mining operations and data centers, with the ability to complement intermittent renewable energy sources. According to Westinghouse, each unit can reduce CO₂ emissions by up to 55,000 metric tons per year compared to equivalent fossil fuel alternatives.
The next step for the eVinci is fueled operation testing at Idaho National Laboratory’s DOME test bed, managed by the National Reactor Innovation Center. Westinghouse aims to begin serial production in 2029, with multiple reactors per year. In parallel, its partnership with Penn State University — which has entered the pre-application phase with the Nuclear Regulatory Commission — targets the installation of an eVinci unit for research and demonstration purposes. The program is advancing on multiple fronts simultaneously, with the stated goal of combining physical testing, modeling, and design iteration to reduce technical risk without sacrificing schedule.
If the timeline holds, eVinci could become the first American commercial microreactor to roll off a true production line. The August test in Nevada is not a finish line — it is confirmation that the design works, and that the next step, fueled operation, is already on the calendar.
